SELECTIVE CATALYTIC REDUCTION OF NO BYC3H6 OVER A COMMERCIAL AUTOMOTIVE IRIDIUM BASED CATALYST

Abstract

Ir/TiO2 coated on cordierite monolith was investigated in the selective catalytic reduction (SCR) of NO with propene using a broad temperature range and simulated diesel exhaust gas conditions under the standard mixture (1000 vpm NO, 2000 vpm C3H6, 500 vpm CO, 10 vol.% O2). The physicochemical characterization of the commercial catalyst showed that the BET surface area of the fresh and aged samples are very low ( 5m2/g). XRD patterns revealed the presence of rutile TiO2 and Ir metallic phases. Irreversible H2 adsorption performed on the fresh and used catalysts indicated a very low accessibility of H2to metallic surface. The catalyst exhibited a significant DeNOx performance (>80% reduction of NO into N2with a selectivity approaching 90% at the end ofheating-up cycle (620°C)). During the cooling-down step, the NO reduction into N2 activity was further weakly decreased (20% loss in DeNOx activity). The commercial automotive catalyst was not stable after hydrothermal treatment (10% H2O/N2, 720°C). The NO-N2 and the NO-NO2 conversions start at a temperature close to that at which the oxidation of CO and C3H6 by oxygen has been already complete. N2 forms under conditions where reductants are fully converted to CO2.